The invention relates to a heat exchanger having improved concentric tubes. Reference is made in particular to heat exchangers used for heating or cooling treatment of fluid food products, either containing solid pieces or not but in any case being liable to pumping, in which the product to be treated circulates in long cylindrical tubes externally of which a heating/cooling covering is provided in which heating or cooling fluid circulates, commonly known as the exchange fluid. The exchange fluid is generally heated water or coolant water. In these kinds of exchangers a hollow axial body is provided internally of the tubes in which the product circulates, in which hollow axial body the exchange fluid is introduced. This hollow body is normally configured such as to define preferential pathways, respectively for the outward and return runs of the exchange fluid, and such as to have the inlet and outlet of the exchange fluid arranged at a same end of the hollow body, while the other end of the body is closed. In general terms, in this type of exchanger the product to be treated circulates in an annular-section cavity defined between the internal wall of the cylindrical tube for product circulation and the external wall of the hollow body arranged internally of the tube. A covering is arranged externally of the circulation tube, such that the product receives or relinquishes heat both from the outside of the tube and from the inside of the tube.
In order to prevent excessive length of the tubes in which the product circulates, the heat exchangers, as can be seen in FIG. 1, are normally constituted by various straight portions, arranged in series, which are crossed by the product which enters the first portion, exits therefrom in order to enter the next, and so on up until it exits from the final portion; these portions however can each reach several meters in length. An inlet connection for the product into the heat is provided, arranged at the start of the first portion of the heat exchanger itself. Intermediate connectors are provided between the various portions of the heat exchanger and are generally U-shaped as the heat exchanger portions are kept parallel to one another and the connectors carry the product to be treated from one portion to the next. These intermediate connectors are provided with flanges which enable the connection to corresponding flanges on the product circulation tubes. Annular seals are provided between the flanges, which guarantee sealing of the connections. Naturally in the infrequent case that the heater had only one portion, U-connectors would not be necessary (realising the outlet connection of the tube of one portion and the inlet connection of the next) but there would instead be an inlet connector and an outlet connector for the product joined to the ends of the cylindrical tube.
The exchange fluid circulating in the various external coverings is inserted in the various coverings, and passes from one mantle to another unproblematically as the external structure of the coverings has no involvement with the trajectory of the product. More complex is the introduction and extraction of the exchange fluid into and from the various hollow bodies present in the tubes crossed by the product, as the structure of the hollow bodies is completely internal of the product flow and the tubes carrying exchange fluid into the hollow bodies have to cross the product flow.
To solve the problem the known-type exchangers prolongs the central hollow body up to bringing it to exit the pathway of the product to be treated; the exit of the prolongation is generally from the intermediate connectors. In this way the exchange fluid can be introduced and extracted into and from the hollow central body without the fluid interfering with the product flow. Naturally the zone of interference between the prolongation of the hollow body and the wall of the intermediate connector must be completely sealed such as to prevent the leaking of the product. This is obtained very simply by making a hole in the connector wall, into which the prolongation of the intermediate hollow body is passed, and by welding the external wall of the prolongation to the peripheral edge of the hole made in the connector.
The known solution exhibits some drawbacks. During the stage of construction it is not very easy to perform the welding between the prolongation of the hollow body and the connector wall correctly as the internal part of the connector is not easily reachable. During the functioning of the heater the product frequently stagnates at dead points in the contact zone between the prolongation of the hollow body and the connector wall; this necessitates frequent cleaning operations of the product pathway, operations which would be much less frequent if the product could circulate freely and if there were not stagnation-prone zones. Further, when it becomes necessary to replace the seals ensuring the seal between the flanges, which has to be done rather frequently, the hollow body, which is welded in a single piece with the connector, has to be completely extracted from the cylindrical tube such as to be able to insert the annular seal from the free side of the hollow body, which is at the opposite end to the end projecting from the connector, or such as to be able to insert the seal in the flange connected to the cylindrical tube. Both the cleaning and replacing operations of the seals lead to a removal of the hollow body from the cylindrical tube. As the hollow body exhibits supports which enable the coaxiality with the tube it is inserted in to be maintained, this removal can lead to a scoring of the inside of the cylindrical tube. Finally, as the U-connectors connect up two portions of the heat exchanger, in order to perform the cleaning and replacing operations of the seals in one alone of the portions, it is necessary to remove the hollow bodies of both portions of the heater and connected by the U-connector from the respective cylindrical tubes.